The present invention relates to a projection display system, and particularly to a picture projecting apparatus for a projection display system and the method thereof which can project a large color picture by a monochrome projection tube only.
A direct type display apparatus generally used such as a CRT is getting larger in its size, but the according rapid increase of the volume and the weight makes it practically impossible to manufacture a Braun tube larger than 45 inch.
Accordingly, a projection display system appears to project an image displayed on a CRT into a large screen so as to make it easier to watch in the distance.
The simplest projection system has a constitution in which images displayed on a picture tube is projected through an optical system on a screen. But, in this system, the deterioration of the resolution makes it not good for the formation of a large picture.
Thus, as shown in FIG. 1, a conventional projection display system has been used, in which the respective red, green and blue of single color images are shown on three monochromic picture tubes or projection tubes 352, 353 and 354, and then are projected through a focusing lens 357 on a screen 351, to form a color picture. However, the requirement of three independent projection tubes in this constitution results in high cost and difficulty of convergence control.
As shown in FIG. 2, another example of conventional projection system is a liquid light valve type picture projection system in which three red, green, and blue liquid crystal display devices LCD1, LCD2 and LCD3 respectively display red, green and blue monochromatic pictures. In this system, a white light generated in a light source LAMP is separated into three red, green, and blue monochromatic lights through mirrors M1 and M2 and dichroic mirrors DM1, DM2 and DM3 and then the separated monochromatic lights are scanned as a driving light for the respective liquid crystal display devices LCD1, LCD2 and LCD3 to form the respective monochromatic pictures, and these monochromatic pictures are projected through a mirror M3 and dichroic mirrors DM3 and DM4, and a lens LE on a screen so as to form a color image. The unexplained reference numerals FIL and C1 to C3 respectively indicates a filter, and focusing lenses of a driving tube.
In this constitution, pictures to be projected are formed on the respective liquid crystal display devices, and the resolution of the system depends on the number of the pixels of the liquid crystal display device. But, currently there is a limitation in increasing the number of the pixels in liquid crystal display devices, so that this system is not appropriate for a high resolution system.